A photodetector is an apparatus comprising a plurality of photodiodes arranged one-dimensionally or two-dimensionally, and an integrating circuit including an amplifier and an integral capacitance part, and may further comprise signal processing circuits subsequent thereto (see for example, Japanese Patent Application Laid-open Gazzete No. H9-270960). With this photodetector, electric charges of amounts that are in accordance with the intensities of light made incident onto the respective photodiodes are output by the photodiodes, these electric charges are accumulated in the integrating capacitance elements, and voltages that are in accordance with the amounts of the accumulated electric charges are output from the integrating circuit. Based on the voltages output from the integrating circuit in accordance with the amounts of electric charges generated at the plurality of photodiodes respectively, the light made incident onto a photodetection surface, on which the plurality of photodiodes are arranged, is detected.